Fringe has spent four seasons dealing with the consequences of "playing God." We've learned all about Walter Bishop's past mistakes, and we've seen him placed alongside dozens of other misguided scientists, whose experiments have threatened people's lives. Over time, all of those foils of Walter Bishop have created a kind of composite portrait of Walter himself.

And now, last night's episode put Walter face-to-face with his ultimate foil: William Bell, his former partner. And we got what will probably be Fringe's ultimate statement on scientific hubris. Spoilers ahead...

I'm assuming that "Brave New World" represents the final, definitive word on the abuses of science, for a couple reasons. First, because I'm not sure where else there is to go after this. And second, because we already know the show is only returning for a shortened season of 13 episodes, and it appears the main focus will be on coping with the Observer invasion and the dystopian future we glimpsed a few weeks ago.

In any case, William Bell's plan is fully revealed in "Brave New World Part 2," and it's just as demented as we all expected. In a nutshell, he has gathered a shipload of Dr. Moreau-esque animal people, like the bat people we saw several weeks ago. And he's going to use Olivia's Cortexiphan powers to collapse both universes, allowing him to create a new universe with whatever laws of physics he desires. This new world will be entirely populated by the weird creatures he's designed, which are safe on board his "Ark," the only point that will survive in both universes.

Why is William Bell doing this? Out of sheer ego and spite. But not the kind of ego that cares about his own survival as an individual. Bell has been dying of cancer, and it's caused him to turn against God, as Walter once did after he failed to save both versions of his son Peter. So Bell wants to become God and give rise to a new universe in his image, as a perverse way of defying his own mortality. He tells Olivia and Peter that he expects to die off in this new world, leaving no humans alive — but he also talks a lot about this act of creation as a way of defying death.

Bell explains:

I grew older. I grew cynical. And I grew cancer. And I realized that dosing myself with Cortexiphan would slow it down. But slowing is not stopping. For me, it's just a matter of time: the clock is ticking. Tick, tick, tick, tick, tick. And that's when it occurred to me: You were right, Walter. Walter, you were right, right, right. Every rant you ever went on made perfect sense. Suddenly, I understood not just you, but everything. God made us in his image. If that is so — if we are capable of being gods — then it is our destiny to do so.

And Bell tells Walter that this was all his idea originally, and he was the one who came up with the plan to collapse both universes — and then Walter asked Bell to cut out a piece of his brain, so "put the genie back in the bottle." Walter may deny it now, but he's "always been playing God," says Belly.

It's all extremely nutty, and an interesting counterpoint to everything we've learned about Walter over the years. We've gone from believing that Walter was simply an arrogant meddler who caused havoc simply out of hubris, to realizing that he was actually motivated by love of his son, in both universes. As we've realized this, the other mad scientists that Fringe has shown us have also been more and more often motivated by compassion or love for family.

So it's jarring that our ultimate reflection of Walter is pure arrogance — and nonsensical arrogance at that. I'm not sure how much of William Bell's scheming and ranting is meant to be nonsense, and how much of it simply comes across that way by accident. But in any case, he's like a crude caricature of Walter, without all the things that have humanized him over the past four years. He wants to create new life, not out of love for that life, but simply to show that he can be a god. He fears his own death, but thinks that creating a whole new world will compensate in some way.

(And yes, Nimoy's William Butler Yeats-quoting, cackling performance is kind of crazily over the top, adding to the impression that this is a scientist who's not just mad, but totally unhinged.)

Olivia's compassion versus her belief in herself

It's a weird thing — in an episode where Walter finally calls Astrid by her real name, nobody calls Olivia by hers. Peter keeps calling her "Liv," a nickname I don't believe he's ever used before. Walter calls her "Olive," something he hasn't called her in years. Nina addresses her as "My dear." It's sort of fitting, in an episode where Olivia is having a bit of an identity crisis.

Olivia feels happiest when she's running to someone's rescue, like when she races off to save Jessica, the victim of last week's nanotech attack. But she's thrown off guard when it turns out that Jessica is actually working for William Bell, and has been yanking Olivia's chain all along to help activate her Cortexiphan powers. She's further unsettled when they interrogate the dead Jessica — in an insanely creepy scene, full of eye-rolling, double voices and weird children's doggerel.

And when Olivia finally connects the dot, and realizes that she, herself, is the power source for William Bell's universe-shattering scheme, she's undone. (A few weeks ago, it took a couple dozen Cortexiphan kids at specific spots, with the bridge between universes open, to collapse the universes — now it just takes Olivia. I guess, because she's more powerful? Or because the universes are already weakened?) Nina tells Olivia that she's so powerful because she has so much compassion, and that's what makes her special. So Olivia's compassion is going to bring William Bell's world of genetically engineered monsters into being.

In the face of this, Olivia feels as though she's still the same trapped little girl that she was, back when Walter and William Bell used to experiment on her in Jacksonville. Now, William Bell is still experimenting on her, and she feels as though nothing has ever changed. Except, Peter points out, that she's not alone this time, because he's there.

At last, Peter and Olivia locate Bell's ark full of freaks, but it takes both of them to reach it. Peter can see it because he's from the other universe, and only Olivia can travel there thanks to her Cortexiphan power. Nina gives Olivia one last pep talk in which she says that Olivia has always had the power — she just has to believe in herself. "You've had the most extraordinary gifts, but the only one you were denied was knowing it. You've had the power all along." (It's sort of a Wizard of Oz moment — she's had the courage all along.)

So Olivia's compassion and her unbridled emotions are what activate her Cortexiphan powers enough to make her a "living uncertainty engine," as Bell puts it. But by believing in herself, Nina suggests, Olivia can put a stop to it. It's like the difference between Olivia's uncontrolled emotions, manipulated by Bell, versus her emotional confidence and control. One means death for the universes, the other means life.

(A side note: I guess we never really see much of Nina reacting to Olivia's memories of their years together being completely gone. Or how Nina feels about William Bell, her best friend, turning out to be a psycho. Nina must be pretty depressed right now.)

In the end, though, Olivia's belief in herself simply allows her and Peter to reach Bell's ship. It's not Olivia that stops Bell's plan, after all. Instead, her identity crisis is resolved in the most direct fashion possible — by Walter putting a bullet in her brain. Which he then digs out, after which her Cortexiphan-soaked brain tissue repairs itself. (Which, I guess, was set up with the lemon cake thing last week.) Olivia's near-death experience burns out her Cortexiphan charge, thwarting Bell's plan — so he uses his bell-eport to get himself the heck out of there. (I like how Nimoy gets to have a holodeck and a transporter in this episode.) (GIF via Vargesz.)

So now that she's had a nice brain-scraping, how does Olivia resolve her feelings over nearly being used to destroy the worlds? We don't get to see much about it. Her only post-mortem scene involves Peter telling Olivia that he's found them a house to live in — and that now that she's fulfilled the prophecy that she must die, he's never going to lose her again. (Good luck with that!) And then she drops the bombshell we've all been expecting: She's pregnant. Cue lots of kissing as Walter and Astrid watch and hug.

I'm kind of sad that instead of getting to assert her own agency, and show once and for all that she's not just a tool of the mad scientists, Olivia's main contribution is to get shot in the head. And then the question of how Olivia feels about having spent her whole life as a plaything of unscrupulous scientists is kind of lost in the shuffle, after having been such a huge point earlier in the episode. On the plus side, we've already met Olivia's kid, and we know she grows up to be pretty kick-ass.

September and the Devil's Trap

You could have been excused for thinking you'd turned to the wrong channel and were watching an episode of Supernatural for a moment there. September, the friendly observer, gets himself caught in a Devil's Trap. Oh wait — "stasis runes." Sorry.

I'm not entirely sure what the business about Jessica trapping and shooting September was about — except that we already saw him shot ages ago, and thus the show had to reveal why and how that happened, so as not to leave any conspicuous loose ends. Jessica traps September while she's also leading Olivia into a trap — and then shoots him, as a means of activating Olivia's TK powers one more time. (Image via Walter's Wonky World.)

In any case, September then spells out what most of us have already guessed — the scene in the Opera House where he tells Olivia that she has to die hasn't happened yet, from his point of view. And he has no clue why she would have to die. He pops off to investigate the future.

Later, an apparently uninjured September crops up in Walter's lab as he's making some peanut-butter-and-jelly sandwiches. (Walter's still puckish after those jello shots at the hospital turned out to be urine samples instead.) September wants Walter to warn the others that "they're coming." Meaning, apparently, the other Observers.

So what was all this about?

To some extent, like I said, this episode was about closing the book on Walter's crimes — thanks to William Bell, we've now seen them writ large, and Walter has had a chance to reject that sort of hubris definitively, with his response spelled out in bullet points. It also probably closes out the book on Olivia and her Cortexiphan experiences, although Walter mutters something about her still having latent biological abilities.

But what was this season, as a whole, about? A couple things, I guess:

1) Putting one last obstacle between Peter and Olivia, and then reaffirming their love once and for all. Peter being removed from the multiverse was a bit of an obstacle to a successful romance, and so was a world where nobody remembered him. But destiny (or "providence," to quote William Bell) brought the two lovers back together once again — and September spent a lot of time explaining that their child is important. Probably because she's the only one who can fight the Observer invasion.

2) Showing the two universes becoming friends — and then facing a threat worse than a war between them. Over the course of the season, the two Olivias went from loathing each other to admiring each other, the two Astrids made friends, and Lincoln traded universes for good. And even the two Walters had a bonding moment by the end. And meanwhile, the threat of the two universes trying to destroy each other was replaced with an even worse threat: that first David Robert Jones, and then William Bell, might collapse both universes to create a new nightmare cosmos full of weird monsters.

All in all, this was by no means the strongest season of Fringe. The rebooted cosmos allowed for some interesting new versions of these familiar characters, but also meant that Walter Bishop was sidelined for a lot of the year. The threat of super-shapeshifters was built up, and then vanished. And so on. But looking on the bright side, the show did manage to spend a year exploring the relationship between the two universes in some often-fascinating ways, and resolved some of its major thematic points in a pretty definitive way. And now we're set for a final season about a dystopian Observer-dominated future. And judging from the glimpse we got a few weeks ago, that could be the most fun yet.